1. Field of the Invention
The present invention relates to a tripod type constant velocity joint mounted to drive axles of a car for transmitting power to drive wheels, and more particularly, the present invention relates to a tripod type constant velocity joint which can reduce frictional resistance generated between a tripod housing and a cylindrical roller which are in contact with each other.
2. Description of the Prior Art
Generally, a constant velocity joint is mounted to drive axles connected to a final reduction gear in a front wheel drive car or a four wheel drive car and functions to transmit power to drive wheels. The constant velocity joint can transmit power due to the fact that a contact point between a drive shaft and a driven shaft exists on a line which bisects an angle between them.
A constant velocity joint consists of a sliding joint, a shaft and a fixed joint. The sliding joint is used for absorbing displacements in X and Y directions in a car, and examples of the sliding joint include a tripod type joint, a double offset type joint, a cross groove type joint, etc. The fixed joint is used for absorbing a steering angle of the car, and examples of the fixed joint include a Rzeppa type joint, a Birfield type joint, etc.
The present invention is concerned with a tripod type constant velocity joint, and therefore, a construction of a tripod type constant velocity joint of the prior art will be described hereinafter with reference to FIGS. 1 through 5.
A tripod type constant velocity joint mounted to drive axles connected to a final reduction gear in a car for transmitting power to drive wheels, as shown in FIGS. 1 through 3, includes a tripod housing 20 which defines an opening. The tripod housing 20 is formed with three track grooves 21 which are communicated with the opening and are uniformly spaced apart from one another in a circumferential direction. Each track groove 21 has a contact groove 22 formed in a side wall section thereof. The contact groove 22 has a bottom wall portion which defines a pair of guide surfaces P and Q which are parallel to each other. A spider 23 is disposed in the opening of the tripod housing 20 and has three trunnions 24 which project from an outer surface thereof to be inserted into the three track grooves 21, respectively. Three pairs of a needle roller 25, a spherical roller 26 and a cylindrical roller 27 are sequentially and diametrically fitted around the three trunnions 24 of the spider 23, respectively. By this, the cylindrical roller 27 is engaged into the contact groove 22. A striker-out 28 and a retainer ring 29 are locked to a threaded portion of each trunnion 24 above the needle roller 25. The striker-out 28 and the retainer ring 29 prevent the cylindrical roller 27 from being released.
In the tripod type constant velocity joint constructed as mentioned above, when the joint is rotated at a certain joint angle, the cylindrical roller 27 engaged into the contact groove 22 defined in the track groove 21 of the tripod housing 20 is rolled on the pair of guide surfaces P and Q of the contact groove 22, and at the same time, the spherical roller 26 absorbs an aligning movement of the cylindrical roller 27.
On the other hand, the cylindrical roller 27 is moved along the pair of guide surfaces P and Q of the contact groove 22 of the tripod housing 20 upon rolling as described above. According to this, as shown in FIG. 4, it is possible to control a direction over a specified angle .beta..
However, the tripod type constant velocity joint of the prior art suffers from defects in that since an upper end surface and a lower end surface of the cylindrical roller 27 are in contact with all of a left lower end contact point A1, a right lower end contact point A2, a right upper end contact point A3 and a left upper end contact point A4 formed in the contact groove 22 of the tripod housing 20 while performing a direction control over the specified angle .beta., a great deal of frictional resistance is generated between the cylindrical roller 27 and the tripod housing 20.
In other words, in the tripod type constant velocity joint as shown in FIG. 5, when assuming that F.sub.1, F.sub.2, F.sub.3, and F.sub.4 are frictional resistance at the contact points A1, A2, A3 and A4, respectively, and l.sub.1, l.sub.2, l.sub.3, and l.sub.4 are distances from a center of the cylindrical roller 27 to the contact points A1, A2, A3 and A4, respectively, since the upper end surface and the lower end surface of the cylindrical roller 27 are in contact with all contact points A1, A2, A3 and A4 formed in the contact groove 22, rotational friction moment M.sub.4 of the cylindrical roller 27 is described by M.sub.4 =F.sub.1 l.sub.1 +F.sub.2 l.sub.2 +F.sub.3 l.sub.3 +F.sub.4 l.sub.4, whereby the frictional resistance cannot but be increased.